1. Field of the Invention
The present invention relates to processes and systems for fracturing a subterranean environs after significant movement of tubulars in a well bore have occurred, and more particularly, to processes and systems for fracturing a subterranean environs wherein a fracturing fluid is used to set packers adjacent an opening in tubing positioned in a subterranean well bore and to fracture a subterranean formation.
2. Description of Related Art
In the production of fluid from a subterranean well, a well bore may be drilled in a generally vertical, deviated or horizontal orientation so as to penetrate one or more subterranean formations. The well is typically equipped by positioning casing which may be made up of tubular joints into the well bore and securing the casing therein by any suitable means, such as cement positioned between the casing and the walls of the well bore. Thereafter, the well may be completed in a typical manner by conveying a perforating gun or other means of penetrating casing to a position that is adjacent the subterranean formation of interest and detonating explosive charges so as to perforate both the casing and the subterranean formation. In this manner, fluid communication may be established between the subterranean formation and the interior of the casing to permit the flow of fluid from the subterranean formation into the well. Production tubing that is equipped with a packer for sealing the annulus between the casing and the production tubing may be run into the well. Care must be taken in lowering the production tubing through the fluid that is present in the well. If the velocity of formation fluid passing the production packer as the production tubing is lowered into the well is too great, the occurrence of severe suction effects or swabbing may cause deformation of the packer resulting in premature setting thereof. Accordingly, care is taken to either lower the production tubing within the well at a low enough rate to ensure against premature setting due to swabbing or to employ a packer that is designed with means, for example internal flow paths and/or mechanical locking mechanisms, that allow it to be lowered at higher speeds. Once positioned in the well, the elastomeric sealing element of the packer can be mechanically or hydraulically expanded into sealing engagement with the casing. Fluid produced from the subterranean formation into the casing can be produced to the surface via the production tubing.
Alternatively, a well may be completed as an “open hole”, meaning that intermediate casing is installed and secured within the well bore by conventional means, such as cement, but terminates above the subterranean formation of interest. Typically, a tubular liner may be positioned within the well bore along the subterranean formation of interest and may be anchored to the intermediate casing near the end of the liner proximate to the well head. As positioned within the well, cement is not employed in the annulus between the tubular liner and the well bore. The well may be subsequently equipped with production tubing or casing and conventional, associated equipment so as to produce fluid from the subterranean formation of interest to the surface. As with a fully cased well, the lower casing or tubular liner may be equipped with one or more packers on the exterior thereof. This well system may also be used to inject fluid into the well to assist in production of fluid therefrom or to inject fluid into the subterranean formation to assist in extracting fluid therefrom.
Further, it is often desirable to stimulate the subterranean formation of interest to enhance production of fluids, such as hydrocarbons, therefrom by pumping fluid under pressure into the well and the surrounding subterranean formation of interest to induce hydraulic fracturing thereof. Thereafter, fluid may be produced from the subterranean formation of interest, into the well bore and through the production tubing and/or casing string to the surface of the earth. Where it is desired to stimulate or fracture the subterranean formation of interest at multiple, spaced apart locations along a well bore penetrating the formation, i.e. along an open hole, isolation means, such as packers, may be actuated in the open hole to isolate each particular location at which injection is to occur from the remaining locations. Thereafter fluid may be pumped under pressure from the surface into the well and the subterranean formation adjacent each isolated location so as to hydraulically fracture the same. The subterranean formation may be hydraulically fractured simultaneously or sequentially. Conventional systems and associated methodology that are used to stimulate subterranean formation in this manner include swellable packer systems with sliding sleeves, hydraulically set packer systems, ball drop systems, and perforate and plug systems.
In conventional open hole operations, many if not all of the isolation packers deployed on a tubular liner may be set substantially concurrently. For example, an isolation packer may include an elastomer which swells upon contact with liquid, such as formation liquid, drilling liquid or other liquids injected into the well. As these packers are set prior to injection of fracturing fluid through the production casing or tubing, the subsequent injection of fracturing fluid at relatively high rates and pressures balloons the tubular liner outwardly thereby causing the same to contract in length. Further, the injection of fracturing fluid from the well head at generally ambient temperatures, e.g. 60° F. to 70° F., and at relatively high rates does not allow sufficient time for the fracturing fluid to warm up to bottom hole temperatures, e.g. 250° F. Thus, the relative cool fracturing fluid causes the tubular liner to contract in length even more. Such contraction, which can amount up to 10 feet or more in length, often may damage the packers that were previously set thereby causing the packers to fail, i.e. leak, thereby allowing fluid communication around the packer in the annulus between the tubular liner and walls of the open hole. Also, the relatively high pressure at which the fracturing fluid is injected often causes the set packers to fail. Previous methods employed to mitigate the effects of such tubing movement, such as the use of expansion joints in the tubular liner, are expensive and have not proved to be reliable. Accordingly, a need exists for processes for stimulating intervals of a subterranean environs at spaced apart locations which minimizes failure and damage to packers used to isolate intervals that may occur due to tubing movement.